Studies on sulfenamides. VI. Cyclic voltammetry and controlled potential electrolysis of 4'-substituted 2-nitrobenzenesulfenanilides in the presence of trifluoroacetic acid or pyridine.

Abstract

Anodic oxidation of 4'-substituted 2-nitrobenzenesulfenanilides (4'-OMe (1a), 4'-Me (1b), 4'-H (1c), 4'-Cl (1d), 4'-COOEt (le), 4'-COCH3 (1f), 4'-NO2 (1g)) and 4'-ethoxycarbonyl-N-methyl-2-nitrobenzenesulfenanilide (1h) was investigated by cyclic voltammetry and controlled potential electrolysis at a glassy-carbon or a reticulated vitreous carbon anode in acetonitrile containing 1% trifluoroacetic acid (TFA) or 1% pyridine. The peak potentials of 1a-g in acetonitrile containing TFA were 0.23-0.55 V more positive than those in acetonitrile containing pyridine. On the other hand, the peak potential of 1h was not affected by addition of TFA or pyridine. This suggests that 1a-g partially dissociate into the sulfenamide anions in the presence of pyridine. Electrolysis of 1a, 1b, and 1d in the presence of TFA gave the corresponding 2, 7-disubstituted phenazines in higher yields than that in the absence of TFA. Although electrolysis of 1e and 1f did not give the corresponding phenazines in the absence of TFA, in the presence of TFA it did. Electrolysis of 1c and 1g did not give the corresponding phenazines in the presence or absence of TFA. Electrolysis of 1a-d in the presence of pyridine gave the corresponding pyridinated sulfenanilides, and that of 1e and 1f gave the corresponding 4, 4'-disubstituted azobenzenes. Electrolysis of 1g gave p-nitroaniline both in the absence and presence of pyridine. The variation of yields of the phenazines and species of the products was explained in terms of the extent of dissociation of the dication intermediate, which in turn depends on the 4'-substituent. The nitrenium ions and nitrenes are suggested to be intermediates in the formation of the corresponding phenazines and the primary amines, respectively. The azobenzenes are considered to be oxidation products of the primary amines.